Dead Jogger's Husband: I Cheated

The husband of murdered North Carolina jogger Nancy Cooper is finally speaking out about the state of his marriage, admitting he cheated and claiming that his wife did, too.

"Three years ago, I made a mistake while married to Nancy," Brad Cooper said in an affidavit filed Wednesday in Cary, N.C., and obtained by ABCNews.com.

"I had a single indiscretion and slept with another woman one time," said Cooper. "I deeply regretted [and still regret] that it happened."

While Cooper does not disclose the name of the woman in question, an affidavit filed by his wife's friends identifies her as Heather Heider-Metour, but does not delve deeper into how Cooper met her or the details of their relationship.

ABCNews.com was unable to contact Heider-Metour for comment.

Family and friends of Cooper's wife have been pointing fingers at her husband since the jogger disappeared just after 7 a.m. on July 12 and was found murdered two days later. They claim Cooper was abusive to his wife and even threatened suicide at one point -- claims Cooper adamantly denies in his affidavit.

Police have not named Cooper, 34, as a suspect or a person of interest in his wife's homicide.

In his affidavit, Cooper also alleges that his wife admitted to having an extramartial affair around the same time that he says he revealed his own indiscretions.

"Nancy admitted that she also had an extramarital relationship while married to me, four years ago," Cooper said in the document. "Nancy insisted that she did nothing wrong, that her relationship with the other man only happened once, it wasn't sexual and that no one even knew his name."

The Coopers were attending marriage counseling, according to the affidavit, but in April 2008 Cooper's wife prepared a separation agreement. At the time of her murder, Cooper had not yet signed the agreement.

Custody Battle Gets Heated

In addition to addressing the state of his failing marriage, Cooper wrote extensively about his ability to care for his two daughters, Bella, 4, and Katie, 2, who have since been in the care of his wife's family after they were awarded emergency custody last week.

The 12-page affidavit goes into extensive detail about Cooper's love for his daughters, asserting that he feeds the girls "well-balanced meals" and even gave his wife a day off on the weekends -- known by the family as "mommy's day off" -- during which he'd care for kids.

Cooper recites the children's schedule meticulously, making a point of what an involved father he was to the girls.

The husband adds that while his children have been taken away from him since his wife's death, the separation papers drafted before the murder made clear that he was to share custody of the daughters.

"Nancy and her attorney agreed that I was a fit and proper parent to have the care, custody and control of the children," Cooper says in the affidavit.

The husband paints an ugly picture of his wife's family, who will petition for permanent custody of the girls in a hearing on Friday. He claims that his mother-in-law, Donna Rentz, has "fallen asleep at the wheel on at least two occasions" and has had "as many as seven major car accidents."

Alice Stubbs, the lawyer representing Nancy Cooper's family, declined to comment on Brad Cooper's affidavit when called by ABCNews.com.